The Optimal Nerve Block for Knee Replacement Surgery

Alex Macario, MD, MBA


July 31, 2015

Discharge Readiness After Tricompartment Knee Arthroplasty: Adductor Canal Versus Femoral Continuous Nerve Blocks—A Dual-Center, Randomized Trial

Machi AT, Sztain JF, Kormylo NJ, et al
Anesthesiology. 2015;123:444-456

Study Summary

This prospective randomized trial studied patients undergoing primary, unilateral knee arthroplasty to determine whether using a catheter to deliver a continuous adductor canal block reduced the interval until a patient is deemed ready for discharge, compared with using a continuous femoral nerve block.

The investigators assumed from other studies that the average time to discharge readiness would be expected to be approximately 39 hours, or just short of 2 days.

The study was conducted at two academic institutions in San Diego, California. Before the surgery, 30 mL of lidocaine 2% were delivered via a perineural catheter placed under ultrasonographic guidance; then, a ropivacaine 0.2% infusion at 6 mL/h was initiated, which was stopped the morning of the third postoperative day. For the surgery itself, 70% of the patients received a general anesthetic and the remainder a spinal anesthetic.

The primary outcome was the time to attainment of all of the following:

  • Adequate analgesia, defined as pain severity of 4 or less on a numeric rating scale of 0-10;

  • Independence from intravenous opioids for at least 12 hours;

  • Ability to independently stand up and sit down; and

  • Unassisted ambulation of at least 30 meters (evaluated using the 6-minute walk test).

Patients had physical therapy twice a day, beginning as early as the afternoon of surgery if they reached the orthopedic wards by 2 PM on the day of surgery.

The study found that patients with an adductor canal catheter (n = 39) reached all four criteria in a median of 55 hours (interquartile range, 42-63 hours), which did not differ meaningfully from the 61 hours (interquartile range, 49-69 hours) among those with a femoral catheter (n = 41) (P = .12).

Although the overall time to discharge was not statistically different, 72% of patients with an adductor canal catheter were able to independently ambulate 30 meters and also independently stand and then sit on postoperative day 1, compared with 27% of patients with a femoral catheter (P < .001).

The femoral catheter group reported average pain during physical therapy sessions of 2 out of 10 on a numeric rating scale, compared with 4 out of 10 in the adductor canal catheter group (P = .02).


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